The present invention relates to actuators, particularly to micromachined actuators, and more particular to micromachined electrostatic vertical actuators, for applications such as optical phase shifting.
In recent years numerous micro electromechanical systems (MEMS) devices have been developed. The laterally driven electrostatic comb resonant structure has become an integrated component in many of these MEMS devices. This same device generates levitation force on the suspended structure due to the asymmetric distribution of electrical fields as a bias voltage is applied. This levitation force is often the source of unwanted out-of-plane motion causing tilting to many laterally-driven sensors and actuators. Instead of suppressing the vertical motion it would be desirable to use this levitation force for controllable small vertical motions (&lt;1.5 .mu.m). Other electrostatic vertical motion sensors and actuators typically utilize the parallel plate capacitor effect which is much more nonlinear in nature and has an unstable region of operation, complicating the fabrication and control of the devices. Mechanical stoppers as well as more complicated electrode configurations are often necessary to fabricate parallel plate vertical actuators.
The present invention utilizes the levitation force for providing controllable small vertical motions (&lt;1.5 .mu.m), and involves a micromachined electrostatic vertical actuator. The present invention can be utilized in various applications involving optical phase shifting, such as Fabry-Perot interferometry or phase shifting-based interferometry. The present invention utilizes a levitation force, such as in electrostatic comb drives, to provide vertical actuation that is relatively linear in actuation for control, and can be readily combined with parallel plate capacitive position sensing for position control, for accurate movement in the submicron to micron ranges, which is desirable in phase modulation instruments.